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                                        [Date]
                                           
[Director name and address]



                   Re: Automatic Share Right Grant

Dear [        ]:

                 Pursuant to the Chiron 1991 Stock Option Plan (the "Plan"), 
Chiron Corporation (the "Company") hereby grants you [     ] restricted share 
rights ("share rights") with respect to its Common Stock ("Common Stock") 
effective[                 ] ("Grant Date").  These share rights are granted to
you in accordance with the terms of this letter and the provisions of the Plan.

                 1.   Each share right entitles you to receive one share of 
Common Stock on the date that the share right vests in accordance with 
paragraph 2 (the "Vesting Date"), if you continue to provide services to the 
Company or its subsidiaries as a director, an employee, a consultant or an
independent contractor through such date.  A certificate representing the 
shares of Common Stock will be issued without restriction on or as soon as 
practicable following the Vesting Date of the share right, provided that such 
share right has not been terminated or canceled before such date.

    Your share rights will vest in five equal annual installments on each of
the first five anniversaries of the Grant Date, provided that, in each case, you
continue to provide services to the Company or its subsidiaries as a director,
an employee, a consultant or an independent contractor through such date.  In
addition, if you terminate your service with the Company by reason of death or
Permanent Disability (as defined below), all your outstanding share rights will
immediately vest in full.  If you cease to provide services to the Company or
its subsidiaries as a director, an employee, a consultant or an independent
contractor for any reason other than death or Permanent Disability, any share
right held by you that has not vested before the date of your termination of
such services will be canceled automatically and will no longer be outstanding
and no shares of Common Stock will be issued hereunder.  "Permanent Disability"
means your inability to engage in any substantial gainful activity by reason of
any medically determinable 

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                                                                         Page 2

physical or mental impairment which is expected to result in death or has lasted
or can be expected to last for a continuous period of twelve (12) months or 
more.  In the event of an agreement to dispose of all or substantially all of
the assets or outstanding capital stock of the Company by means of a sale,
merger, reorganization, or liquidation, all of your outstanding share rights
will immediately vest.  However, no acceleration of vesting will occur if the
terms of the agreement require as a prerequisite to the consummation of any such
sale, merger, reorganization or liquidation that your share rights will be
either assumed by the successor corporation or parent thereof or be replaced
with a comparable award subject to shares of the successor corporation or parent
thereof.  Upon consummation of the sale, merger, reorganization or liquidation
contemplated by the agreement, share rights, whether or not accelerated, will
terminate unless assumed pursuant to a written agreement by the successor
corporation or parent thereof.

              Your share rights hereunder may not be sold, assigned,
transferred, alienated, subject to garnishment or otherwise encumbered in any
manner other than by transfer by will or the laws of descent and distribution. 
In the event of your death before the issuance of shares of Common Stock under
your share rights, any shares issuable thereunder by reason of your death will
pass pursuant to your will or by the laws of descent and distribution.

              The issuance of shares of Common Stock hereunder is subject to
the procurement by the Company of all approvals and permits required by
regulatory authorities having jurisdiction over the share rights and stock to be
issued hereunder.  The inability of the Company to obtain approval from any
regulatory body having authority deemed by the Company to be necessary to the
lawful issuance of any Common Stock hereunder will relieve the Company of any
liability with respect to the non-issuance of the Common Stock as to which such
approval is not obtained.  The Company, however, will use its best efforts to
obtain all such approvals.

              If any change is made to the Common Stock issuable hereunder by
reason of any stock split, stock dividend, recapitalization, combination of
shares, exchange of shares or other change affecting the outstanding Common
Stock as a class without receipt of consideration, the Compensation Committee of
the Board of Directors of the Company (the "Compensation Committee") will make
appropriate adjustments to such share rights to prevent the enlargement or
dilution of your rights thereunder.

              Neither you nor, in the event of your death, your beneficiary
will have any rights as a shareholder with respect to the shares of Common Stock
issuable hereunder until you have been issued a stock certificate for such
shares.  It is the intention of the parties that the Company's obligations under
your share rights are unfunded for purposes of the Internal Revenue Code and
that the Employee Retirement Income Security Act of 1974 does not apply to your
share rights.

              This agreement does not constitute a contract of employment or
services.  Neither the grant of this share right, nor any action taken under the
terms of this share right or the Plan, nor any provision of this share right or
the Plan will be construed to grant you the right to remain in the employ or
service of the Company (or any subsidiary or parent of the Company) for any
period of specific duration.

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                                                                          Page 3

    If the foregoing is satisfactory, please sign, date, and return the enclosed
copy of this letter to_______________________________________________

                                                       Very truly yours,

                                                       CHIRON CORPORATION

                                                       By 
                                                          --------------------





AGREED AND ACCEPTED: 

----------------------

[Director]